Spatial and vertical distribution of radiocesium in seawater of the East China Sea.

The 137 Cs activity in surface water of the East China Sea (ECS) was 0.66-1.36 Bq m-3 during May of 2011. The low activities were observed in the Changjiang Estuary and Zhejiang-Fujian coast and high activities were observed in the south offshore and Kuroshio Current pathway, suggesting that the influence from the current system in the ECS. The 134 Cs were undetectable (<0.03 Bq m-3 ) and the contribution of the Fukushima accident to ECS is estimated to be below 3%; hence it is negligible during the investigation period. Using the vertical profiles of 137 Cs in the ECS, the mass balance is obtained, which suggests that the oceanic input dominates the 137 Cs source in the ECS. 137 Cs is potentially useful to trace water mass movement in the ECS. Our study provides comprehensive baseline of 137 Cs in the ECS for evaluation of the possible influence of the nuclear power plants in the future.